This invention relates to power supply apparatuses and power supply operational methods.
Electrochemical devices are utilized in an increasing number of applications, such as personal digital assistants (PDAs), mobile telephone devices, notebook computers, electronic gaming devices, music players, etc. Electrochemical devices which are rechargeable are typically utilized in conjunction with some form of charge and discharge control. Some control implementations utilize one or more power MOSFET to provide charging and/or discharging of an electrochemical device. When a power FET is enabled, the channel resistance is a function of the voltage applied between the gate and the source (Vgs) of the FET. A lower resistance is provided with increasing Vgs voltages. During high rates of discharge of the electrochemical device or when the charge of the electrochemical device voltage has degraded a sufficient amount, the xe2x80x9conxe2x80x9d resistance of the power FET switching device increases. Such causes the voltage on the battery terminal to be lowered by an amount equal to the load current times the channel resistance (Rdson for drain to source resistance) for the power MOSFET(s).
Electrochemical devices are typically used in applications having specific parameters for proper operation. An often overlooked issue in safety circuits in such applications is the total impedance due to the channel resistance (Rdson) of the power MOSFETs used to control charge and discharge currents. The total Rdson of a power MOSFET is related to the voltage applied between the gate and the source of the FET (Vgs), the current through the device, and the temperature of the device. As the voltage of the electrochemical device falls, Vgs applied to the gate is diminished which in turn causes Rdson to increase. Decreasing voltage of the electrochemical device also corresponds to a higher current to the load in as much as power consumption is assumed to be constant (i.e., VI is a constant quantity). From an external device perspective, such results in a lower voltage due to the drop across the power MOSFET and an additional power loss equal to I2Rdson. The additional power loss is translated into heat which also causes the channel resistance to increase.
Customers or engineers of applications utilizing electrochemical devices account for such performance degradation by setting cut-off voltages for the electrochemical devices at abnormally high levels to assure proper operation. Improved apparatuses and methodologies for providing electrical energy which alleviate problems of arrangements utilizing abnormally high cut-off voltages are desired.